This invention relates to centrifugal pumps and especially to nuclear reactor recirculation pumps which pump radioactive demineralized water at elevated temperatures, as for example, about 530.degree. F. to about 570.degree. F. and elevated pressures, as for example, about 1500 psi to about 2500 psi. The vapors of the pumped liquid may also be toxic. Pumps of this nature comprise a generally cylindrical case with an intake port and a discharge port, and housing a centrifugal impeller. A volute or scroll in the case conducts pumped liquid to the discharge port. The case is capped by a generally cylindrical cover plate, such that a joint is formed therebetween. The cover plate has a central opening for passage of a driven shaft to which the impeller is connected and may house a shaft bearing. An annular gasket or primary seal constructed of metal and asbestos, one form of which is known as "Flexitallic," is positioned between the case and its cover plate to substantially prevent leakage of pumped liquid across the joint and to the atmosphere. Because the vapors of the pumped liquid may be toxic, it is imperative that such leakage be almost, if not completely, eliminated.
In the past, the cover plate has been welded to the case when the primary seal leaks. Failures of the welds have been experienced because of movement, even limited, of the cover plate relative to the case due to operating conditions, such as the effects of pressure and temperature. Failure of the welds have also been experienced because of joint imperfections.
More recently, as a solution to the leakage problem, it has been proposed to weld a one piece, relatively inflexible, cast or machined member to the case and the cover. The member is constructed to bridge the joint between the case and the cover. Here again, this seal can fail because of its lack of flexibility.